As the power of tractors and agricultural efficiency has increased, agricultural implements such as planters have increased in span, or width, to accommodate larger numbers of individual row units. Large planters generally include a main frame having a forward hitch assembly for drawing by a tractor and left and right wing sections pivotally attached to a portion of the main frame. The pivoting wing connections allow the wings to fold relative to the main frame for transport and storage of the planter. Early planters pivotally displaced the wings vertically to reduce planter width and provide clearance for transport through narrow spaces.
However, as the size of planters has increased, planter wings are generally folded in a forward direction to accommodate longer planter wings. This evolution has necessitated the incorporation of telescoping hitch assemblies and specific folding functions to accommodate planter wings of increased length. The telescoping hitch assemblies allow components of the hitch to be inserted within each other to vary the length between the hitch and the main frame. Therefore, the longer the wing sections, the longer the tongue will have to telescope to accommodate folding of the wings. This causes the transport wheels of the main frame to be extended away from the tractor.
As the planters are getting larger and heavier, it is becoming more difficult to be able to transport these machines to and from the field. Forward folding planters are prone to extreme hitch weight on the tractor and a large turning radius due to the long wheelbase between the tractor tires or tracks and the planter transport tires. This long wheelbase is because the transport tires of the planter are also used to set the height of the frame during planting to keep the row units at a height so the machine will plant at a uniform depth. The ideal location for the tires to level the frame height is between the row units. This location of the tires also provides that the planter does not account for negative hitch weight on the tractor when the planter is unfolded and the row units are off the ground.
Methods exist to shorten the wheelbase between the tractor tires and the planter transport tires. For instance, some planters include a sliding transport axle at the main frame of the planter. The axle is able to slide along the tongue to move toward and away from the rear of the tractor to alter the wheelbase. However, it can be very difficult to cause the axle to slide, especially when seed, fertilizer, insecticide, or other material weighs down the planter. The sliding action can cause increase wear and stress to the main frame of the implement, while also adding complexity to the machine. Furthermore, as the components of planters are commonly made from metals, there exists a chance that rusting or deformation could occur, which could prevent the axle from being able to slide along the tongue.
U.S. Pat. No. 6,408,950 to Shoup (the '950 patent) discloses a planter having an independent support wheel assembly that is slideable towards the a new center of gravity after the frame has moved from an extended or working position to a folded or transport position. However, the '950 patent includes the use of two separate motor mechanisms and wheel systems. Each of the motor mechanisms includes separate cylinders to raise and lower separate wheels. Therefore, one wheel may be lowered while the other is raised. However, the wheels must be raised and lowered individually. The separate motor mechanisms, wheels, and cylinders will also take up much space and will add a great deal of weight to the planter. The addition of multiple moving assemblies and parts also increases the chances that a moving component can fail or become damaged, which will affect the use of the planter. The multiple moving parts also increase the cost and complexity of the machine and the operation thereof.
Therefore, there is a need in the art of agricultural equipment for a method and apparatus for adjusting the wheelbase length between tractor wheel and implement transport wheel and accommodating a shift of the center of gravity of the implement that is simple to operate. There is also a need in the art for a method and apparatus for adjusting the wheelbase length and accommodating a shift of the center of gravity that will not increase the weight and cost of the implement, while also being effective.